Southeast Fisheries Science Center John Lamkin, Trika Gerard*, Estrella Malca, Aki Shiroza, Barb Muhling, Natasha Davis, Francisco Fuenmayor, Samantha Whitcraft Atlantic Oceanographic and Meteorological Laboratory Libby Johns*, Ryan Smith, Nelson Melo, Grant Rawson University of the Virgin Islands Nasseer Idrisi, Tyler Smith, Kevin Brown USVI Larval Reef Fish Supply Study: 2007-08 Report Funded by : NOAA Coral Reef Conservation Program. PRB-08-09-12 Contact : [email protected] 2 The U.S. Virgin Islands (USVI), comprised of St. Thomas, St. John, and St. Croix, are located on a geological shelf surrounded by an extensive Caribbean tropical marine ecosystem. This ecosystem contains a mosaic of critical habitats that support productive local fisheries. Nearshore “nursery habitats” such as sea grasses, mangroves, and associated coral reefs, provide vital foraging, predator refuge, and spawning habitat for over 400 species of fish found in the Virgin Islands. Red Hind and Grammanik Banks, located 14 km south of St. Thomas, provide habitat for multi-species spawning aggregation sites and a healthy, deep coral reef system (35- 40 m) for economically important coral reef fish including red hind, yellow fin grouper, Nassau grouper, tiger grouper, and dog snapper. Fishing pressure at these suspected sources of larval recruits prompted the Caribbean Fisheries Manage- ment Council to close the Grammanik Bank seasonally from February through April, and GRAMMANIK RED HIND CLOSED CLOSURE designate Red Hind Bank a AREA permanently closed Marine Conservation District (MCD). Banks contiguous with these protected areas provide similar habitats and contain reported spawning aggregation sites. Unfortunately, neither the biological nor the physical processes which drive production on the banks, nor the larval transport pathways connecting the banks, the protected areas, nor the flows across the banks, have been quantified. Absent such knowledge, management decisions (including the designation of MCD and/or seasonal closures) are based on historical knowledge and best professional judgment, rather than quantifiable, scientific information. To address this data gap, National Oceanic and Atmospheric Administration (NOAA) scientists from the Southeast Fisheries Science Center (SEFSC) and the Atlantic Oceanographic and Meteorological Laboratory (AOML) in Miami, Florida, working with scientists from the University of the Virgin Islands (UVI) and the Virgin Islands Department of Planning and Natural Resources, Division of Fish and Wildlife (VIDPNR), designed and executed a three-year interdisciplinary pilot research project consisting of two major components: research cruises and inshore studies. Funding for this research was provided by NOAA’s Coral Reef Conservation Program (CRCP). 3 Research Cruises The first component consisted of research cruises using the NOAA Ship Nancy Foster to conduct biological and physical oceanographic surveys of the USVI bank ecosystems and surrounding regional waters. A total of three research cruises were conducted from 2007 to 2009 (See 2009 cruise report attached). These cruises focused on reef fish larvae in association with an ocean- ographic (biological, physical and chemical) survey of the bank system, coral reef environs and inshore waters of the USVI. The cruise track from the first cruise, conducted March 28 through April 9, 2007, is shown in Figure1. Station locations for the 48 stations taken in this portion of the cruise, in addition to the locations where seven satellite-tracked surface drifters were deployed, are marked on the figure (an additional set of stations were collected farther to the west, west and south of Puerto Rico, not shown). As shown in Figure 1, detailed surveying was conducted south of the USVI and British Virgin Islands (BVI); a section was done across Anegada Passage, and less spatially intensive sampling was conducted in the upstream region of the Leeward Islands and along the northern edge of Saba Bank. Figure 1. Cruise track, station locations and drifter deployment sites for Year 1, March 28 – April 9, 2007. The cruise track from the second cruise, conducted March 11 through March 24, 2008, is shown in Figure 2 Station locations from the 76 CTD casts, 6 surface drifter deployments, and biological sampling are shown. As can be seen in Figure 2, the sampling protocol in 2008 was similar to that of 2007, with the addition of sampling to the north of the U. S. and British Virgin Islands and Anegada Island, and a transit across Saba Bank to the southeast. 4 Figure 2. Cruise track, station locations and drifter deployment sites for Year 2, March 11-24, 2008. In order to understand larval dispersion and transport it is necessary to develop regional larval transport models and integrate mesoscale physical oceanographic observations. This was accomplished by shipboard measurements combined with real-time satellite imagery and satellite-tracked surface drifters. This allows biological sampling to be adapted to physical oceanographic conditions at appropriate time scales. As this study expands, future surveys will include sampling around the islands of St. Croix, Vieques, and Culebra. Inshore Study The second component of this research was shore-based collections of post settlement fishes in nursery habitats such as mangroves, sea grasses, and patch reefs, using small boat operations. Shore-based sampling was conducted once per year in years 2007 and 2008 to investigate the connectivity between coastal nursery habitats and adult habitats offshore. The project is focused on critical reef fish species that are heavily fished throughout the study region and directed at answering one broad question: How are unprotected USVI banks, fisheries managed areas such as the Red Hind Bank Marine Conservation District, seasonally closed areas such as the Grammanik Bank, and inshore areas ecologically linked via reef fish larval dispersal, transport, and life-history patterns? To begin answering this question, we surveyed water properties, currents, and dispersal and transport of settlement-stage fish larvae around the USVI and neighboring regions. We also surveyed near shore habitats for newly settled larval recruits. These surveys will yield an understanding of regional spatial variation in the supply of settlement-stage fishes and the relative importance of Grammanik Bank and other areas as sources of juvenile fishes recruiting to the waters of the USVI. This project will provide fisheries 5 independent data and valuable tools for resource management, and will assist in developing an integrated ecosystem-scale assessment of coral reef-based fisheries. Physical Oceanographic Processes The upper level currents of the Caribbean Sea form the southwestern limb of the North Atlantic Subtropical Gyre, flowing primarily to the west-northwest as part of the geostrophic western boundary current system, with a superimposed northward surface component due to the non- geostrophic Ekman forcing of the easterly trade winds. On average, these currents (Figure 3) are organized into a broad, weak Antilles Current which runs to the northwest along the northern side of the Virgin Islands, Puerto Rico, Hispaniola, and the Bahamas, and a stronger Caribbean Current which enters the Caribbean Sea through the Windward Islands, flowing westward and then northward at the Yucatan coastline to form the Yucatan Current, which in turn becomes the Loop Current in the Gulf of Mexico and finally the Florida Current/Gulf Stream as it exits the Gulf of Mexico through the Florida Straits. Several quasi-permanent gyres are found along the path of the Caribbean Current, mostly obviously in Figure 3 in the area just northwest of Panama near 80 W, known as the Panama-Colombia Gyre. Thus, the average regional currents surrounding the study area for the USVI Larval Distribution and Supply Study generally describe a splitting of the westward flow around the Virgin Islands and Puerto Rico, with the portion to the north taking the shorter Antilles Current route towards the northern Bahamas, and the portion to the south joining the Caribbean Current. Ultimately both branches of the average currents join up as the Gulf Stream north of the Bahamas (Figure 3). However, these average current maps do not describe the synoptic situation, i.e. the currents that may be found at any particular time. On the contrary, this region of the northeast Caribbean Sea is dominated by smaller-scale eddies and gyres as illustrated by the synoptic run of the Naval Research Laboratory (NRL) Global Numerical Layered Ocean Model shown in Figure 4. This typical example of surface current speed and direction shows that, while in the western portion of the Caribbean the currents are indeed organized into fairly strong and continuous flows associated with the Caribbean-Yucatan-Loop Current system, the situation in the eastern Caribbean is not as clear and the flow appears to be dominated by eddy variability. In other words, while on average the currents appear relatively simple as in Figure 3, in reality if one were to sample at a particular time the situation would be significantly more complex as shown in Figure 4. 6 Figure 3. Average ocean surface currents from historical ship drift analysis from the US Coast Guard's Mariano Global Surface Velocity Analysis. The lower panel highlights the Antilles Current, and the upper panel highlights the Caribbean Current. (for more information see http://oceancurrents.rsmas.miami.edu/data.html ). 7 Figure 4. Naval Research Laboratory